1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor wafer, particularly relates to a method for manufacturing a semiconductor wafer having a single crystal semiconductor layer over an insulating film, a semiconductor device using a semiconductor wafer having a single crystal semiconductor layer over an insulating film, and a method for manufacturing such a semiconductor device.
Note that in the present specification, “semiconductor devices” refers to devices in general, which can operate by utilizing semiconductor properties, and electro-optic devices, semiconductor circuits; electronic devices are all included in the category of semiconductor devices.
2. Description of the Related Art
Formation of a single crystal semiconductor layer over an insulating film is widely known as an SOI (silicon on insulator) technology. An SOI structure is a structure in which a silicon oxide film is embedded in a single crystal silicon substrate and a single crystal silicon thin film is provided thereover. A substrate having such an SOI structure is also referred to as an SOI substrate.
When an SOI structure used, since there is an insulating film below an element, a device isolation process can be simplified as compared with the case where an element is formed over a bulk silicon wafer; therefore, the number of process steps can be reduced. Further, semiconductor integrated circuits using an SOI substrate have been attracting attention because parasitic capacitance between a drain and a substrate in a transistor is reduced and the performance of the semiconductor integrated circuits is improved.
As a method for manufacturing an SOI substrate, for example, a hydrogen ion implantation separation method disclosed in Reference 1 (U.S. Pat. No. 6,372,609) is known. In a hydrogen ion implantation separation method, hydrogen ions are implanted in a silicon wafer by an ion implantation method, and thereby a microbubble layer is formed at a predetermined depth from the surface, and a thin silicon layer (SOI layer) is bonded to another silicon wafer using the microbubble layer as a cleavage plane. In addition to the heat treatment for separating an SOI layer, an oxide film is formed on the SOI layer by heat treatment in an oxidizing atmosphere and then, the oxide film is removed, and after that heat treatment is performed at 1000° C. to 1300° C. in a reducing atmosphere to increase bonding strength and reduce surface roughness.
An ion implantation method is also referred to as an ion introduction method, in which particles to be introduced into a sample in vacuum are ionized and accelerated by direct current or high frequency. An ion implanter using an ion implantation method includes an ion source, a mass separation unit, an acceleration unit, a beam scanner (electrostatic scan) unit, an introduction chamber (end-station), and an evacuation unit. Further, since an ion beam is not uniform, scanning with an ion beam is performed electrically in order to obtain uniformity of a surface of the sample. The introduced particles have a Gaussian distribution in the depth direction.
Further, Reference 2 (Japanese Published Patent Application No. 2000-12864) is known as an example of a semiconductor device using an SOI substrate. Reference 2 also discloses a technique in which hydrogen is introduced by an ion implantation method.
Further, Reference 3 (Japanese Published Patent Application No. H10-162770) discloses a linear doping apparatus by which a substrate is transferred without rotation.